Systems and methods for protecting a sensitive device from corrosion

ABSTRACT

A method for protecting a magnetic head according to one embodiment includes reducing a relative humidity in a vicinity of a magnetic head by passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below a threshold level for reducing or eliminating corrosion of the sensor. Additional methods are also presented.

RELATED APPLICATIONS

This application is a continuation in part of U.S. patent application Ser. No. 12/115,449, filed May 5, 2008, and which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to data storage systems, and more particularly, this invention relates to magnetic heads for tape drives, and coatings to prevent corrosion thereon.

BACKGROUND OF THE INVENTION

In magnetic storage systems, data is read from and written onto magnetic recording media utilizing magnetic transducers commonly. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.

An important and continuing goal in the data storage industry is that of increasing the density of data stored on a medium. For tape storage systems, that goal has lead to increasing the track density on recording tape, and decreasing the thickness of the magnetic tape medium. However, the development of small footprint, higher performance tape drive systems has created various problems in the design of a tape head assembly for use in such systems.

In a tape drive system, magnetic tape is moved over the surface of the tape head at high speed. This movement generally must skive off the air between the tape and the tape bearing surface (TBS) of the head in order to achieve a low spacing between the head sensor and the magnetic coating on the tape. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the magnetic tape is crucial to minimize signal amplitude decrease from Wallace spacing losses, which increase with increased magnetic recording flux densities. Thus the TBS is in contact with the tape so that the read element is in near contact with the tape to provide effective coupling of the magnetic field from the tape to the read element. The Wallace spacing is, among other factors, due to asperities on the tape and to erosion of the sensor due to wear. Build up of non-magnetic material between the sensor and the tape magnetic coating can also cause Wallace spacing. Corrosion or oxidation initiated at the TBS of the sensor or the protective poles surrounding the sensor can also lead to Wallace spacing losses.

Further, the AMR, GMR, TMR, etc. sensors usable in tape heads all have a propensity for corrosion. Corrosion or oxidation of the sensor at the TBS can result in surface oxidation of the sensor metals which result in an increase in the spacing between the magnetically active portion of the sensor and the magnetic coating on the tape. High level corrosion can completely destroy the magnetic response of the sensor. One proposed solution is to recess the sensor and apply a hard protective overcoat, e.g., of alumina. However, such materials are in contact with the tape, and tend to wear away, thereby leaving the sensor unprotected. The methods of depositing the hard protective coatings require large expensive tools which preclude the reapplication of a hard coating once it has been worn off. Further, such recession results in Wallace spacing signal losses, which are exacerbated the higher the density of the recorded data on the media.

For tape heads, sensors can be recessed and flux guided, but flux guides have not worked well due to head processing difficulty and to spacing loss.

Alternatively, GMR heads may be fabricated using materials that have improved corrosion resistance, but these materials may not provide optimal magnetic performance (amplitude in particular).

Head-media stiction is usually addressed by making the media rougher, but this may adversely affect the signal-to-noise ratio and thus detection capability and ultimately areal density.

SUMMARY OF THE INVENTION

A method for protecting a magnetic head according to one embodiment includes reducing a relative humidity in a vicinity of a magnetic head by passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below a threshold level for reducing or eliminating corrosion of the sensor.

A method for protecting a magnetic head according to another embodiment includes, during a reading operation, setting potentials of a sensor and a substrate of the sensor to about a common value; and during an idle period, raising the potential of the substrate to a level above that of the sensor.

A method for protecting a magnetic head according to yet another embodiment includes detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and if the detected relative humidity is above the threshold level, passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below the threshold level for reducing or eliminating corrosion of the sensor.

A method for protecting a magnetic head according to yet another embodiment includes detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and setting a potential of the sensor at some value relative to the substrate or the surrounding materials based on the comparison.

Any of these embodiments may be implemented in a magnetic data storage system such as a tape drive system, which may include a magnetic head, a drive mechanism for passing a magnetic medium (e.g., recording tape) over the magnetic head, and a controller electrically coupled to the magnetic head.

Other aspects, advantages and embodiments of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a simplified tape drive system according to one embodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional, two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a detailed view of a partial tape bearing surface of a pair of modules.

FIG. 3 is a flow diagram of a method according to one embodiment.

FIG. 4 is a flow diagram of a method according to one embodiment.

FIG. 5 is a flow diagram of a method according to one embodiment.

FIG. 6 is a flow diagram of a method according to one embodiment.

FIG. 7A is a schematic diagram of a tape portion including an applicator portion according to one embodiment.

FIG. 7B is a schematic diagram of a tape portion including a cleaning portion according to one embodiment.

FIG. 7C is a schematic diagram of a tape portion including an applicator portion and a cleaning portion according to one embodiment.

FIG. 8A is a simplified side view drawing of a tape drive system with a tape engaging the head.

FIG. 8B is a simplified side view drawing of a tape drive system with a tape spaced from the head and an applicator engaging the head.

FIG. 9A is a chart of corrosive effects on an uncoated 16-channel head subjected to a corrosive environment, plotting change in resistance (in %) versus time elapsed (in hours).

FIG. 9B is a chart of corrosive effects on a 16-channel head coated with squalane subjected to a corrosive environment, plotting change in resistance (in %) versus time elapsed (in hours).

FIG. 9C is a chart of corrosive effects on a 16-channel head coated with squalane subjected to a more corrosive environment, plotting change in resistance (in %) versus time elapsed (in hours).

FIG. 10 is a chart of scaled resistance versus current squared (in mA²).

FIG. 11 is a chart of thermal conductance (in mW/° C.) versus stripe height (in μm).

FIG. 12 is a chart of resistance (in ohms) versus time (in hours) showing the effects of corrosion on sensors.

FIG. 13 is a chart of resistance (in ohms) versus time (in hours) showing a resistance of corrosion by sensors.

FIG. 14 is a simplified schematic diagram of a tape drive system according to one embodiment.

FIG. 15 is a flow chart of a method for protecting a magnetic head according to one embodiment.

FIG. 16 is a flow chart of a method for protecting a magnetic head according to one embodiment.

FIG. 17 is a flow chart of a method for protecting a magnetic head according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

The following description discloses several preferred embodiments of tape-based storage systems, as well as operation and/or component parts thereof.

In one general embodiment, a method for protecting a magnetic head comprises applying an organic coating to a magnetic head for reducing exposure of the head to oxidation promoting materials, and storing the magnetic head.

In another general embodiment, a method for protecting a magnetic head of a magnetic storage system comprises applying an organic coating to a magnetic head for reducing exposure of the head to oxidation promoting or corrosive materials, the organic coating being applied to the magnetic head after the head is installed in the magnetic storage system. The coating also reduces the exposure of the head to moisture (H₂O) which is an essential molecule to promote corrosion.

In another general embodiment, a method comprises fabricating a tape having an applicator portion for applying an organic coating to a magnetic head for reducing exposure of the head to oxidation promoting or corrosive materials, applying the organic coating to the applicator portion of the tape, and applying a lubricant to a data portion of the tape.

In yet another general embodiment, a method comprises fabricating a tape having a data portion and a cleaning portion for removing an organic coating from a magnetic head.

In a further general embodiment, a method comprises reducing a relative humidity in a vicinity of a magnetic head by passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below a predetermined threshold (also referred to herein as a “clip level”) for reducing or eliminating corrosion of the magnetic head.

A method for protecting a magnetic head according to another general embodiment includes, during a reading operation, setting potentials of a sensor and a substrate of the sensor to about a common value; and during an idle period, raising the potential of the substrate to a level above that of the sensor. The potential of the sensor during the idle period may be set at either at about a same value as the potential of the sensor during the reading operation, or set higher or lower than the potential of the sensor during the reading operation.

A method for protecting a magnetic head according to yet another general embodiment includes detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and if the detected relative humidity is above the threshold level, passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below the threshold level for reducing or eliminating corrosion of the sensor.

A method for protecting a magnetic head according to yet another general embodiment includes detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and setting a potential of the sensor at some value relative to the substrate or the surrounding materials based on the comparison.

FIG. 1 illustrates a simplified tape drive 100 of a tape-based data storage system, which may be employed in the context of the present invention. While one specific implementation of a tape drive is shown in FIG. 1, it should be noted that the embodiments described herein may be implemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 are provided to support a tape 122. One or more of the reels may form part of a removable cassette and are not necessarily part of the system 100. The tape drive, such as that illustrated in FIG. 1, may further include drive motor(s) to drive the tape supply cartridge 120 and the take-up reel 121 to move the tape 122 over a tape head 126 of any type.

Guides 125 guide the tape 122 across the tape head 126. Such tape head 126 is in turn coupled to a controller assembly 128 via a cable 130. The controller 128 typically controls head functions such as servo following, writing, reading, etc. The cable 130 may include read/write circuits to transmit data to the head 126 to be recorded on the tape 122 and to receive data read by the head 126 from the tape 122. An actuator 132 controls position of the head 126 relative to the tape 122. The remaining components of the simplified tape drive 100 will be discussed in reference to a specific embodiment of the system.

An interface may also be provided for communication between the tape drive and a host (integral or external) to send and receive the data and for controlling the operation of the tape drive and communicating the status of the tape drive to the host, all as will be understood by those of skill in the art.

By way of example, FIG. 2 illustrates a side view of a flat-lapped, bi-directional, two-module magnetic tape head 200 which may be implemented in the context of the present invention. As shown, the head includes a pair of bases 202, each equipped with a module 204, and fixed at a small angle α with respect to each other. The bases are typically “U-beams” that are adhesively coupled together. Each module 204 includes a substrate 204A and a closure 204B with a gap 206 comprising readers and/or writers situated therebetween. In use, a tape 208 is moved over the modules 204 along a media (tape) bearing surface 209 in the manner shown for reading and writing data on the tape 208 using the readers and writers. The wrap angle θ of the tape 208 at edges going onto and exiting the flat media support surfaces 209 are usually between ⅛ degree and 4½ degrees.

The substrates 204A are typically constructed of a wear resistant material, such as a ceramic. The closures 204B made of the same or similar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback configuration. The readers and writers may also be arranged in an interleaved configuration. Alternatively, each array of channels may be readers or writers only. Any of these arrays may contain one or more servo readers.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules 204 taken from Line 2A of FIG. 2. A representative tape 208 is shown in dashed lines. The module 204 is preferably long enough to be able to support the tape as the head steps between data bands.

In this example, the tape 208 includes 12-22 data bands, e.g., with 16 data bands and 17 servo tracks 210, as shown in FIG. 2A on a one-half inch wide tape 208. The data bands are defined between servo tracks 210. Each data band may include a number of data tracks, for example 96 data tracks (not shown). During read/write operations, the elements 206 are positioned within one of the data bands. Outer readers, sometimes called servo readers, read the servo tracks 210. The servo signals are in turn used to keep the elements 206 aligned with a particular track during the read/write operations.

FIG. 2B depicts a plurality of read and/or write elements 206 formed in a gap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the array of elements 206 includes, for example, 16 writers 214, 16 readers 216 and two servo readers 212, though the number of elements may vary. Illustrative embodiments include 8, 16, 32, and 40 elements per array 206. A preferred embodiment includes 16 readers per array and/or 16 writers per array. This allows the tape to travel more slowly, thereby reducing speed-induced tracking and mechanical difficulties. While the readers and writers may be arranged in a piggyback configuration as shown in FIG. 2B, the readers 216 and writers 214 may also be arranged in an interleaved configuration. Alternatively, each array of elements 206 may be readers or writers only, and the arrays may contain one or more servo readers 212. As noted by considering FIGS. 2 and 2A-B together, each module 204 may include a complementary set of elements 206 for such things as bi-directional reading and writing, read-while-write capability, backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complimentary modules of a magnetic tape head 200 according to one embodiment. In this embodiment, each module has a plurality of read/write (R/W) pairs in a piggyback configuration formed on a common substrate 204A and an optional electrically insulative layer 236. The writers, exemplified by the write head 214 and the readers, exemplified by the read head 216, are aligned parallel to a direction of travel of a tape medium thereacross to form an R/W pair, exemplified by the R/W pair 222.

Several R/W pairs 222 may be present, such as 8, 16, 32, 64 pairs, etc. The R/W pairs 222 as shown are linearly aligned in a direction generally perpendicular to a direction of tape travel thereacross. However, the pairs may also be aligned diagonally, etc. Servo readers 212 are positioned on the outside of the array of R/W pairs, the function of which is well known.

Generally, the magnetic tape medium moves in either a forward or reverse direction as indicated by arrow 220. The magnetic tape medium and head assembly 200 operate in a transducing relationship in the manner well-known in the art. The piggybacked MR head assembly 200 includes two thin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present between closures 204B thereof (partially shown) to form a single physical unit to provide read-while-write capability by activating the writer of the leading module and reader of the trailing module aligned with the writer of the leading module parallel to the direction of tape travel relative thereto. When a module 224, 226 of a piggyback head 200 is constricted, layers are formed in the gap 218 created above an electrically conductive substrate 204A (partially shown), e.g., of AlTiC, in generally the following order for the R/W pairs 222: an insulating layer 236, a first shield 232 typically of an iron alloy such as NiFe (permalloy), CZT or Al—Fe—Si (Sendust), a sensor 234 for sensing a data track on a magnetic medium, a second shield 238 typically of a nickel-iron alloy (e.g., 80/20 Permalloy), first and second writer pole tips 228, 230, and a coil (not shown).

The first and second writer poles 228, 230 may be fabricated from high magnetic moment materials such as 45/55 NiFe. Magnetoresistive (MR) sensors, such as AMR, GMR and TMR are multi-layer metals, which include, among other metals and alloys: NiFe alloys, Cu, Ru, Co, CoFe alloys, PtMn alloys, IrMn alloys, as well as others. Note that these materials are provided by way of example only, and other materials may be used. Additional layers such as insulation between the shields and/or pole tips and an insulation layer surrounding the sensor may be present. Illustrative materials for the insulation include alumina and other oxides, insulative polymers, etc.

Referring now to FIG. 3, a method 300 for protecting a magnetic head according to one embodiment is described. As an option, the present method 300 may be implemented in the context of the functionality and architecture of FIGS. 1-2C. Of course, however, the method 300 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

In operation 302, an organic coating is applied to a magnetic head for reducing exposure of the head to oxidation promoting materials, such as water, oxygen, chlorine, bromine, sulfur, sulfides, dihydrogen sulfide, sulfur dioxide, nitrogen dioxide, and other corrosive contaminants.

The coating may be formed of virtually any protective material. Illustrative materials of which the coating may be comprised include squalane, butyl stearate, paraffins, polyvinyl chlorides, polyfluorinated films, polyvinylidene fluorides, fatty acid esters, polyurethanes, etc.

In another embodiment, the coating may comprise a tape lubricant, which may be applied separately or come from a portion of the tape such as the leading portion, trailing portion, or middle portion of the tape. In such an embodiment, the amount of tape lubricant present on the portion of the tape is preferably in excess of what is present on the other portion(s) of the tape so as to apply an amount effective to minimize or prevent corrosion.

As alluded to above, the coating may be applied to the magnetic head by a tape. In one approach, the tape may have a portion that is designed to apply the coating as it is run over the head, preferably while the tape is engaged with the head in a tape drive system, feeding the tape from a tape supply cartridge, possibly shown as tape supply cartridge 120 in FIG. 1. This tape may be designed to be used with standard tape drive systems, and may be loaded on a standard size tape supply cartridge.

In another approach, the tape that applies the coating to the magnetic head may include an applicator portion and a data portion. FIG. 7A shows one possible tape with applicator portion approach according to one embodiment. In this embodiment, the tape 710 has a data portion 708 and may be used as a normal data tape, but also may apply the protective coating prior to, after, or in between normal operations as a data tape. Also, the coating may be applied on a routine basis using the applicator portion 704, such as after a preset head running time, after a tape head traverse distance is reached (the total distance that the tape 710 has traveled over the head in both directions), etc. In addition, the applicator portion 704 may comprise less magnetic portion of the tape 710 relative to the data portion 708.

In another approach, the coating is applied to the magnetic head, and after a period of inactivity. Prior to using the magnetic head, the coating is preferably removed. Removal of the coating prior to use on tape, though may not be necessary, as the tape may rub the coating off and the additional magnetic spacing between the sensor and the magnetic coating of the tape may be low enough as to not substantially degrade the performance of the head. This can be useful, for example, if the magnetic head will be stored, shipped, or subject to conditions that might include oxidization promoting or corrosive materials, such as water, oxygen, chorine, and other contaminants, etc. Prior to use, the coating may be removed by a cleaning portion on a tape which is adapted to remove the coating. By “removed” what is meant is that a significant portion of the coating is detached from the head, such as at least 10%, at least 25%, at least 50%, etc. Further, the coating may be completely removed. Once the coating is removed, the head may be used to read and write magnetic data to the tape. After operation of the magnetic head is suspended, another coating may be applied by running a tape across the head, the tape including an applicator portion. Alternatively, other approaches for applying the coating may be used.

In yet another approach, the tape includes a cleaning portion and a data portion. FIG. 7B shows one possible tape with cleaning portion approach according to one embodiment. The cleaning portion 706 may comprise less magnetic material than the data portion 708. The cleaning portion 706 may be on the leading portion of the tape 710, as shown in FIG. 7B, or it may be on the back portion of the tape 710, so that the tape 710 must be unwound from the tape supply cartridge 702 before the cleaning portion 706 is reached. The cleaning portion 706 may also be included somewhere in the middle of the tape 710, or in several locations in the middle of the tape 710. The cleaning portion 706 may also be located in some or all of these locations on the same tape 710.

In another approach, the magnetic tape 710 may comprise a cleaning portion 706 for removing a coating from a head, an applicator portion 704 for applying a coating to a head, and a data portion 708, as shown in FIG. 7C.

Another approach may use an applicator to apply the coating, such as a brush, stamp pad, web, nonwoven material, dropper, injector, etc. The applicator may be comprised of any suitable material. Illustrative materials include fabric, impregnated rubber, foam, etc.

In another embodiment, as shown in FIG. 8B, the applicator 808 may be present in a drive or magnetic storage system 800 in which the magnetic head 802 resides. Also, the applicator may rub across the magnetic head.

In another embodiment, the applicator which is present in a drive in which the magnetic head resides presses against the magnetic head without substantial wiping. For example, the applicator stamps the magnetic head with a minimum amount of wiping, e.g., wipes less than ½ the width of the tape bearing surface measured perpendicular to the direction of media travel the thereacross.

In operation 304, the magnetic head is stored. The head may be stored for many reasons such as prior to assembly in a tape drive system, after assembly and before shipment, after shipment but before use, etc. The coating may also be applied to the magnetic head during building or during packaging (e.g., for shipping, storage, or sale), or during both building and packaging of a drive in which the magnetic head resides to protect the head from corrosion promoting materials.

FIG. 4 illustrates a method 400 for protecting a magnetic head of a magnetic storage system according to another embodiment. As an option, the present method 400 may be implemented in the context of the functionality and architecture of FIGS. 1-3. Of course, however, the method 400 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

In operation 402, a magnetic head is installed in a magnetic storage system. FIG. 8A is an exemplary drawing of a magnetic storage system 800 which has a magnetic head 802 already installed.

In operation 404, an organic coating is applied to a magnetic head for reducing exposure of the head to oxidation promoting materials such as water, oxygen, contaminants, etc.

In one particularly preferred embodiment, the coating may be comprised of a material selected from a group consisting of squalane, butyl stearate, a paraffin, a polyvinyl chloride, a polyfluorinated film, a polyvinylidene fluoride, a fatty acid ester, and a polyurethane.

In another embodiment, the coating may comprise a tape lubricant, which may be applied separately or come from a portion of a tape such as the leading portion, trailing portion, or middle portion of the tape.

FIG. 5 illustrates a method 500 according to another embodiment. As an option, the present method 500 may be implemented in the context of the functionality and architecture of FIGS. 1-4. Of course, however, the method 500 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

In operation 502, a tape is fabricated having an applicator portion for applying an organic coating to a magnetic head for reducing exposure of the head to oxidation promoting materials such as water, oxygen, contaminants, etc.

In operation 504, the organic coating is applied to the applicator portion of the tape. This organic coating is then capable of being applied to a head to protect the head from oxidation promoting materials.

In operation 506, a lubricant is applied to a data portion of the tape. This lubricant can enable the data portion of the tape to run more smoothly over a head.

In one particularly preferred embodiment, the coating may be comprised of a material selected from a group consisting of squalane, butyl stearate, a paraffin, a polyvinyl chloride, a polyfluorinated film, a polyvinylidene fluoride, a fatty acid ester, and a polyurethane.

In another approach, the tape may include at least one of a data portion, an applicator portion, and a cleaning portion.

In another embodiment, the lubricant has a different composition than the coating.

FIG. 6 illustrates a method 600 according to another embodiment. As an option, the present method 600 may be implemented in the context of the functionality and architecture of FIGS. 1-5. Of course, however, the method 600 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

In operation 602, a tape is fabricated having a data portion and a cleaning portion for removing an organic coating from a magnetic head. FIG. 7B shows one embodiment of a tape fabricated according to the method 600.

In one embodiment, the tape is a data tape which has an extended leader portion that can rub the coating off the head prior to using the tape as a data tape.

In another embodiment, the tape is a special tape with a leader specially designed to remove the coating from the head when the tape is loaded onto the tape drive system. In this embodiment, the tape may then have an applicator portion which can reapply the coating to the head when the tape is unloaded from the tape drive system. A tape may have both a cleaning leader portion and an applicator portion to remove the coating from a head when loaded, and reapply the coating to a head when unloaded.

FIG. 7A shows a tape 710 having an applicator portion 704 for applying a coating to a magnetic head for protecting the head from corrosion promoting materials such as water, oxygen, contaminants, etc., according to one embodiment. The tape 710 is housed on a tape supply cartridge 702 and may include a data portion 708 in addition to the applicator portion 704. Although the applicator portion 704 is shown on the leading portion of the tape 710, it may be present at other locations such as in the middle of the tape 710, at the end of the tape 710, in the middle of the tape 710, or at multiple locations on the same tape 710.

FIG. 7B shows a tape 710 having a cleaning portion 706 for removing a coating from a magnetic head according to one embodiment. The tape 710 is housed on a tape supply cartridge 702 and may include a data portion 708 in addition to the cleaning portion 706. Although the cleaning portion 706 is shown on the leading portion of the tape 710, it may be present at other locations such as in the middle of the tape 710, at the end of the tape 710, in the middle of the tape 710, or at multiple locations on the same tape 710.

FIG. 7C shows a tape 710 having an applicator portion 704 and a cleaning portion 706 according to one embodiment. The tape 710 is housed on a tape supply cartridge 702 and may include a data portion 708 in addition to the applicator portion 704 and cleaning portion 706. Although the applicator portion 704 and cleaning portion 706 are shown on the leading portion of the tape 710, they may be present at other locations such as in the middle of the tape 710, at the end of the tape 710, in the middle of the tape 710, or at multiple locations on the same tape 710. The portions may also be separated, and do not necessarily appear on the tape 710 in the order shown in FIG. 7C (for example, the applicator portion 704 may be located closer to the leading edge of the tape 710 than the cleaning portion 706).

FIG. 8A is an exemplary diagram of a tape drive system 800. As shown, the system includes a tape head 802, and a guide mechanism 804 for passing a magnetic recording tape 806 over the head. The system 800 is in read and/or write mode in this diagram. During normal operation, the tape 806 is guided from one reel 814, across the head 802 by the guide mechanism 804, and to a second reel 816. The guide mechanism 804 may include guides 812 such as rotational guides (e.g., rollers), nonrotational guides, etc. on one or more sides of the head 802. As shown, the guide mechanism 804 includes four rollers. It should be noted that any type of guide mechanism known in the art can be used in various permutations.

In one example, the guide mechanism 804 includes at least one guide 812 that moves away from the head 802 to create the relative spacing between the tape 806 and the head 802 as indicated by the arrows.

FIG. 8B illustrates one embodiment of a system that may use one of the methods. During an applying operation, while the tape 806 is adjacent the head 802, a relative spacing between the tape 806 and the head 802 is created before the applicator 808 applies the coating to the head 802. Such a relative spacing is shown in FIG. 8B, and an illustrative position of the applicator 808 when inserted into the spacing.

Preferably, the applicator 808 does not contact the tape 806 during coating application to the head 802, though contact might occur in some embodiments. Non-contact embodiments are preferred so as to avoid any applicator-induced damage to the tape 806 that could otherwise occur. The tape surface is susceptible to scratching damage, and so the tape head 802 is fabricated with smooth surfaces, and generally no abrupt discontinuities that might scratch the tape 806. It follows that an object (not part of the guide mechanism) engaging the tape 806 should also be at least as smooth as the head 802. In addition, there is less chance of debris being transferred from the applicator 808 to the tape 806 if there is no contact therewith.

FIGS. 9A-9C are charts displaying results of experiments conducted on 16-channel heads with and without coatings in different atmospheric conditions. Temperature effects on the resistance of the readers was not accounted for in the measurements.

FIG. 9A is a chart of an uncoated multi-channel GMR head in a static chamber at about 20° C. and about 80% relative humidity (RH) with about 2.5 parts-per-million (ppm) Hydrogen Chloride (HCl). The resistances of 14 readers are measured at consistent time intervals after a baseline is established by letting the resistance normalize after a few hours in the chamber at 80% RH. Then, HCl gas is injected into the chamber at a level of about 2.5 ppm HCl. The change in resistance (in %) is on the y-axis versus the time elapsed in the chamber (in hours) on the x-axis. The change in resistance is determined by dividing the current resistance measured by the baseline resistance measured after normalization. The legend on the right of the chart indicates the reader number for each of the readers tested (14 readers on this multi-channel head were tested. Note that the choice of 14 readers was done due to limitations of the data collection system). As this chart shows, when exposed to a corrosive environment, the resistances of the readers change drastically and unpredictably. This indicates that the head experienced corrosion due to exposure to the corrosive environment.

FIG. 9B is a chart of a multi-channel GMR head coated with squalane in a static chamber at about 20° C. and about 80% RH with about 2.5 ppm gaseous HCl. The resistances of 13 readers are measured at consistent time intervals after a baseline is established by letting the resistance normalize after a few hours in the chamber at 80% RH. Then, HCl gas is injected into the chamber at a level of about 2.5 ppm HCl. The change in resistance (in %) is on the y-axis versus the time elapsed in the chamber (in hours) on the x-axis. According to the legend on the right of the chart, 13 readers on this multi-channel head were tested. As this chart shows, when exposed to a corrosive environment, the readers coated with squalane experienced very little resistance change over the 60 hours of exposure to the corrosive environment. This indicates that the head experienced little or no corrosion over the testing period. When removed from the testing chamber, no corrosion was observed.

In FIG. 9C, the environment was made even more corrosive by increasing the concentration of HCl to about 10 ppm. Here, a multi-channel GMR head coated with squalane was placed in a static chamber at about 21° C. and about 40% RH with about 10 ppm HCl. The resistances of 14 readers are measured at consistent time intervals after a baseline was established by letting the resistance normalize after a few hours in the chamber at 40% RH. Then, the atmosphere in the chamber was altered so that it becomes about 10 ppm HCl. The change in resistance (in %) is on the y-axis versus the time elapsed in the chamber (in hours) on the x-axis. According to the legend on the right of the chart, 14 readers on this multi-channel head were tested. As this chart shows, when exposed to a more corrosive environment than in the test shown in FIG. 9A, the readers coated with squalane experienced very little resistance change over the approximately 25 hours of exposure to the more corrosive environment. This indicates that the head experienced little or no corrosion over the testing period. When removed from the testing chamber, no corrosion was observed.

Another problem encountered with bare heads is that the sensors are susceptible to failure due to shield-shorting as a result of running magnetic recording tape thereacross at low humidity, which is found to produce bridges of conductive material on the MR element and shields. On the flip side, high humidity may result in increased probability of corrosion.

Looking first at the problem encountered at low humidity, a magnetic tape is typically a multilayer structure including a base layer and a magnetically definable layer in which data is stored. The magnetically definable layer includes pure metal particles that define the magnetic transitions that represent data. In addition to encapsulation, binders, etc., the pure metal particles typically represent about 50% of the material in the magnetically definable layer.

One problem frequently encountered during reading and writing to tape is that the metal particles can come loose from the tape and adhere to the head, forming metallic bridges on the head. Read sensors are particularly susceptible to failure due to shield-shorting as a result of bridging. Accumulation has been found to be particularly prevalent in low humidity conditions, e.g., less than about 20% relative humidity. Such low humidity conditions are typical with the current prevalence of air conditioned server rooms and business places.

Known solutions to the bridging problem are to recess the sensor so that its components do not make electrical contact with the conductive accumulation, and/or to coat the head with a durable wear coating. In the former case, such a recessed sensor has not been implemented and is believed to be difficult to manufacture, and would also result in an undesirable spacing loss. The latter method is complex and expensive and the coatings may wear off over time, even with pre-recession. Another means of minimizing the formation of bridging metals has been found to be maintaining all parts at the TBS at the same electrical potential (voltage), referred to as mid-point potential. It should be noted also that the metal bridging phenomenon predominantly occurs in a dry atmosphere.

Referring next to the high humidity situation, excessive relative humidity should also be avoided so as to minimize corrosion of the metals in the readers and other corrodible portions of the head, such as the reader shields and writer poles. Corrosion of the shields and poles leads to spacing loss and broader written transitions than written by the head at initial use. Corrosion of the readers leads to degraded signal amplitudes and spacing losses.

There is accordingly a clearly-felt need in the art for a tape drive system that is less susceptible to shorting due to metallic accumulation on the head and damage of the transducers due to corrosion. It would be desirable to provide solutions that are inexpensive and reliable and solve both problems. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.

In one general embodiment, a method for protecting a magnetic head comprises reducing a relative humidity in a vicinity of a magnetic head by passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being higher than an operating bias current used when the sensor is in use for reading data. The additional heating caused by the elevated bias current reduces the relative humidity in the vicinity of the head. The heating may be induced based on some criteria, e.g., humidity level, or simply applied periodically, or when the sensor is not in use, or for some other reason. One objection to the elevated bias currents while the drive is not writing or reading data is the added power consumption, which though minor, could be important when trying to develop drives with extremely low power consumptions.

In another general embodiment, a method for protecting a magnetic head comprises detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and if the detected relative humidity is above the threshold level, passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being higher than an operating bias current used when the sensor is in use for reading data. The additional heating caused by the elevated bias current reduces the relative humidity in the vicinity of the head.

In yet another general embodiment, a method for protecting a magnetic head comprises detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and setting a potential of the sensor at a value below that of a substrate thereof when the relative humidity in the vicinity of the head is above a threshold level. While this method does not affect the relative humidity in the vicinity of the head, the differing potentials assist in preventing corrosion at high humidity. More description of the method is presented below. One draw-back of dropping the potential of the sensor below that of the substrate to protect against corrosion is that in dry environments, shorting has been show to increase when the sensor is at a different voltage than the substrate. Since corrosion occurs in humid environments, if one detects the humidity, then one can choose to toggle between a low voltage for the sensor in humid environments and a substantially similar voltage to the substrate in dry environments.

In order to choose a bias current to depress the local humidity of the reader, it is necessary to determine the temperature versus bias current of the reader. For sheet films of metals, the stripe (sheet) temperatures of the reader can be determined in Equations 1a through 1d by measuring the stripe resistance (R_(mr)) with the lead and hard-bias resistances (R_(lead)) removed:

R _(mr) =R _(total) −R _(lead)  Equation 1a

R _(mr)(ΔT _(mr))=R _(mro)[(1+α_(mr) *ΔT _(mr))−d _(gmr)(ΔT _(mr))cos(θ)  Equation 1b

δ_(gmr)(ΔT _(mr))=d _(gmro)exp(ρΔT _(mr))=δ_(gmro)exp(−ΔT _(mr)/400° C.)  Equation 1c

where

R _(mro) =R _(sheet) *W/H  Equation 1d

The first term in Equation 1b is the standard temperature dependence of the stripe resistance, with α_(mr) measured to be 0.15° C.⁻¹, and R_(sheet) is 16.4 Ω/sq. ΔT_(mr) is the temperature rise above ambient temperature (25° C.). The second term in Equation 1b is the GMR component to the resistance with δ_(gmr)(ΔT_(mr)) being the temperature dependent fractional GMR resistance when the pinned layer (M_(PL)) and the free layer (M_(FL)) magnetization are anti-parallel, and θ is the angle between M_(P2) and M_(FL). H and W are the stripe height and the track width, respectively. In normal operation, M_(P2) and M_(FL) are designed to be almost perpendicular. The deviation from perpendicularity is due to the rotation of M_(FL) by M_(P1) (φ_(PL)) and the magnetic field generated by the bias current (H_(cFL)). H_(cFL) is given by Equation 2:

H_(cFL)≡εI_(mr)M_(FLHB)  Equation 2

The angle q is given by Equation 3:

−cos(θ)=sin(φ)˜−εI _(mr)  Equation 3

The stripe temperature rise versus bias current (I_(mr)) is assumed to be proportional to the power in the stripe, which can be determined with Equation 4:

ΔT _(mr) =R _(mr)(ΔT _(mr))I ² _(mr)/κ_(mr)  Equation 4

κ_(mr), termed the thermal conductance, completely defines the sensor Joule heating. Combining Equations 1a-1d and Equations 2 through 4 yields Equations 5a through 5c:

ΔT _(mr)=(γ_(mr)/α_(mr))I ² _(mr)[1−εδ_(gmr) I _(mr)]/[1−γ_(mr) I ² _(mr)]  Equation 5a

R _(mr) =R _(mro)[1−εδ_(gmr) I _(mr)]/[1−γ_(mr) I ² _(mr)]  Equation 5b

with

κ_(mr)=α_(mr) R _(mr)(I _(mr)=0)/γ_(mr)  Equation 5c

Equation 5b can be transformed into a linear equation by first defining a scaled function, as shown in Equation 6:

R _(scale) =[R _(hot)(I _(mr))−R _(hot)(I _(mr)=0)]/R _(hot)(I _(mr))  Equation 6

Then R_(mr)(I_(mr)) and R_(mr)(−I_(mr)) can be combined as shown in Equation 7:

R _(mrC) =[R _(mr)(I _(mr))+R _(mr)(−I _(mr))]/2=R _(mro)/[1−γ_(mr) I ² _(mr)]  Equation 7

Replacing R_(hot) by R_(mrC) in Equation 7 yields Equation 8:

[R _(mrC)(I _(mr))−R _(mrC)(I _(mr)=0)]/R _(mrC)(I _(mr))=γ_(mr) I ² _(mr)  Equation 8

FIG. 10 shows a plot of R_(scale) versus I² _(mr) using R_(mrC)(I_(mr)), R_(mr)(I_(mr)) and R_(mr)(−I_(mr)) for R_(hot)(I_(mr)) with δ_(gmr)=0.13, ε=0.025/mA and ρ=0.0025° C.⁻¹. κ_(mr), derived from data using Equations 5c and 8, is fit to a second order equation in H and W in Equation 9:

κ_(mr)=κ_(equ)=κ_(W) W+κ _(H) H  Equation 9

where κ_(equ) is the equilibrium form of κ_(mr). The fits are shown in FIG. 11, where κ_(W)=11.0 W/m/° C. and k_(H)=40.4 W/m/° C. The parameters used here are found to work for the sheet sensors tested. For different sensors, the parameters, and even the functional forms may be different. The user will need to determine how to measure the temperature versus current or power or voltage of the sensors they use.

When the stripes are exposed to elevated temperatures, the resistance will change due to irreversible thermodynamic processes, while κ_(mr) will remain constant. Thus, during thermal stress testing, the temperature is determined using the parameter κ_(mr) and the measured power in the stripe. Furthermore, these parameters can be used to project for any geometry what the temperature versus current will be. Using the parameters given above and Equations 1 through 9, the Joule heating temperature rise (ΔT_(mr)) versus bias current for a reader with an H of 1 μm and a W of 4 μm is given in

TABLE 1 Joule heating temperature rise versus bias current of a GMR sensor with the parameters given in the text above and an H of 1 μm and a W of 4 μm. Equations 1-19 are used. Also shown is the local relative humidity for the readers when the surrounding air is at 22° C. and an RH_(a) of 80%. I_(mr) (mA) 1 2 3 4 5 6 ΔT_(mr) (° C.) 0.8 3.1 7.0 12.5 19.7 28.6 RH_(I,) (%) 76.5 67.3 54.1 39.3 26.7 16.3

FIG. 12 is a plot of the change in resistance for GMR sensors biased with a 1 mA bias current while exposed to hydrochloric acid (HCl) gas at a level of 2 injections of 20 ppm and an environment of about 22° C. with 80% R.H. As this plot shows, the resistances for each of the reported sensors, R16, R22, R24, and R28, increased greatly the longer the sensors were exposed to the corrosive gases in a humid environment. This is due to corrosion of the sensors.

FIG. 13 is a plot of the change in resistance (in %) for GMR sensors biased with a 5 mA bias current while exposed to hydrochloric acid (HCl) gas at a level of 2 injections of 20 ppm and an environment of about 22° C. with 80% R.H. As this plot shows, the resistances for each of the reported sensors, R03, R07, R15, and R23, stayed relatively constant or changed minimally over the course of the exposure to the harsh environment. This is probably due to the bias current applied to the sensors reducing the amount of corrosion the sensors experienced.

Corrosion is accelerated by relative humidity. Relative humidity is a percentage of the humidity in the air relative to the saturation point at a given temperature (100% R.H. point). The saturation vapor content (V_(sat)) versus temperature, T (Kelvin) is given by Equation 10:

V _(sat)(T)=2.672×10⁸e^(−4845/T)  Equation 10

For a given relative humidity (RH_(a)) value and ambient temperature T_(aK), the vapor content is given by Equation 11:

V _(RHa)(T _(aK))=(RH_(a)/100%)V _(sat)(T _(aK))=(RH_(a)/100)2.672×10⁸e^(−4845/TaK)  Equation 11

If a device is heated above the ambient temperature by DT_(J), then the local relative humidity of the device, RH_(L), is given by Equations 12a through 12c:

RH_(L)=100%[V _(RHa)(T _(aK))V _(RHa)(T _(aK) +ΔT _(J))]  Equation 12a

RH_(L)=RH_(a)e^(4845[(1/TaK)−(1/(TaK+ΔTj))])  Equation 12b

RH_(L)˜RH_(a)e^(−(4845/TaK)(ΔTj/TaK))  Equation 12c

This heating of the device can change the relative humidity such that problems associated with high relative humidity and low relative humidity can be avoided or minimized, such as corrosion of sensor components due to high relative humidity. Table 1 shows the local relative humidity, RH_(L) when the air temperature is 22° C. and the air relative humidity is RH_(a) 80% for bias currents of 1, 2, 3, 4, 5 and 6 mA for a sensor with an H of 1 μm and a W of 4 μm and the thermal properties described above.

Alternatively, the Joule heating temperature required to depress the relative humidity from RH_(a) to RH_(L) when the air temperature is T_(aK) is:

ΔTj˜T_(aK)*(T_(aK)/4845)*ln(RH_(a)/RH_(L)),  Equation 13

where ln(x) is the logarithm of x in base e. Table 2 gives the Joule heating temperature rise. With this example, a bias current of 5 mA will drop the sensor local relative humidity to 30% or below for humidity levels of 80% at temperatures of 40° C. and below.

TABLE 2 Joule heating temperature rise required to drop the local relative humidity of a GMR reader to an RH_(1.) of 30% from an ambient value of RH_(a) for a GMR sensor with the parameters given in the text above and an H of 1 μm and a W of 4 μm. Equation 13 is used. The ambient temperatures are given in oC. (T_(aC) = T_(aK) − 273). RH_(a) T_(aC) (° C.) 20 25 30 35 40 40% ΔT_(J) (° C.) 5.1 5.3 5.5 5.6 5.8 50% ΔT_(J) (° C.) 9.1 9.4 9.7 10.0 10.3 60% ΔT_(J) (° C.) 12.3 12.7 13.1 13.4 14.0 70% ΔT_(J) (° C.) 15.0 15.5 16.0 16.6 17.1 80% ΔT_(J) (° C.) 17.4 18.0 18.6 19.2 19.8 90% ΔT_(J) (° C.) 19.5 20.1 20.8 21.5 22.2

Accordingly, with reference to FIG. 14, a method for protecting a magnetic head may be incorporated into an illustrative system 1400. The illustrative system 1400 may include a controller 128 or other circuit or system for reducing a relative humidity of a magnetic head 126 by passing an elevated bias current through a sensor of the head 126 during at least some time periods when the sensor is not in use for reading data, the elevated bias current being higher than an operating bias current used when the sensor is in use for reading data. The elevated bias temperature induces Joule heating in the head, which in turn warms the air in the vicinity of the head, thereby lowering the relative humidity in the vicinity of the head.

With continued reference to FIG. 14, the extent to which the relative humidity is changed in the vicinity of the head 126 may be based at least in part on an ambient humidity. Humidity may be measured in the drive, outside the drive, or both. In addition, temperature may be measured in the drive, outside the drive, or both, such as with a thermometer, thermocouple, resistance temperature detector (RTD), etc. The measured relative humidity may be compared to a threshold humidity level. An elevated bias current may be passed through the sensor when the relative humidity in the vicinity of the head 126 is above a threshold level. Also, the controller 128 may refrain from passing an elevated bias current through the sensor when the relative humidity in the vicinity of the head 126 is below a threshold level. The threshold level may be the same for both high and low humidity, or may be different threshold levels for each condition.

Table 2 gives examples Joule heating temperatures for a selected environments to depress the sensor relative humidity to 30%. Table 1 shows the local relative humidity, RH_(L) of a GMR reader with an H of 1 μm and a W of 4 μm and the thermal properties described above when the air temperature is 22° C. and the air relative humidity is RH_(a) 80% for bias currents of 1, 2, 3, 4, 5 and 6 mA.

Another means of protecting the sensor against corrosion is to set the sensor at a voltage which is negative relative to the substrate and other materials at the TBS. At high humidity, sensor electrical potential differences (voltage) should be adjusted to a value that is typically lower than the tape 122 (and/or substrate) voltage. More negative voltages are preferable as humidity increases.

In any of the embodiments presented herein, any type of humidity measuring device or sensor 150 known in the art may be used to estimate or measure the relative humidity. For example, a digital humidity sensor for sensing humidity may be located in the vicinity of the head and/or outside the drive housing. Illustrative humidity sensors include the HC 105 and HC 109 capacitve SMD humidity sensor sold by E+E Electronik, Langwiesen 7, A-4209 Engerwitzdorf, Austria (www.epluse.com); and the G-Cap-U capacitive relative humidity sensor and EMD series relative humidity sensor sold by General Electric having a sales office and address of GE Sensing, 1055 Mission Court, Fremont, Calif. 94539 (www.gesensing.com).

Note that if the humidity sensor is in the drive housing itself, a larger delay between readings is acceptable, as humidity changes in the drive may be relatively slow.

Now referring to FIG. 15, a method 1500 for protecting a magnetic head, according to one embodiment, is shown. As an option, the present method 1500 may be implemented in the context of the functionality and architecture of FIG. 14. Of course, the method 1500 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

With continued reference to FIG. 15, in operation 1502, a relative humidity in a vicinity of a magnetic head (e.g., in the drive housing, adjacent to the head, etc.) may be reduced by passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, where the elevated bias current may be, but does not necessarily have to be, higher than an operating bias current used when the sensor is in use for reading data. The elevated bias current is chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below some threshold, which may be predetermined, selected dynamically, etc. for reducing or eliminating corrosion of the magnetic head, especially the sensor. Accordingly, “elevated bias current” as used herein with respect to this and other embodiments refers to a bias current at any level greater than zero, where such level may be lower, higher or the same as a nominal bias current used during reading of data.

In another embodiment, the relative humidity in the vicinity of the head may be detected and compared to the threshold level. Any type of relative humidity sensing device may be used to detecting the relative humidity in the vicinity of the head. One or more threshold levels may also be used for comparing the detected relative humidity against.

Now referring to FIG. 16, a method 1600 for protecting a magnetic head, according to one embodiment, is shown. As an option, the present method 1600 may be implemented in the context of the functionality and architecture of FIG. 14. Of course, the method 1600 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

In operation 1602, a relative humidity in a vicinity of a magnetic head may be detected. As previously mentioned, any type of humidity sensor may be used.

In operation 1604, the detected relative humidity may be compared to a threshold level. Once again, one or more threshold levels may be used for comparing the detected relative humidity against.

In operation 1606, if the detected relative humidity is above the threshold level, an elevated bias current may be passed through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below the threshold level for reducing or eliminating corrosion of the sensor.

In one embodiment, the elevated bias current is not passed through the sensor when the relative humidity in the vicinity of the head is below the threshold level.

In addition to adjusting the relative humidity, or alternatively thereto, the potential of the sensor may be adjusted to reduce the probability of shorting aid/or corrosion. At low humidity, e.g., at or below a low threshold level, such as below about 40% relative humidity, the system may adjust the potential of the sensor so that sensor voltage about matches the substrate voltage (assuming the substrate is conductive) and/or MR shield and/or writer pole voltages. By matching sensor and tape or substrate voltages as closely as possible, shield-shorting as a result of bridging can be minimized. Conversely, at higher humidity levels, the potential of the sensor may be set negatively relative to the substrate voltage and/or MR shield and/or writer pole voltages. For metals, such as MR sensors, both elevated humidity levels and corrosive agents are required to corrode the metals in the sensors. At low relative humidity levels, corrosion can be inhibited or greatly reduced, even with high levels of corrosive agents. In the absence of corrosive agents, GMR sensors can be robust against corrosion, even at high temperatures and relative humidity levels. Doan et al showed that at 80° C. and 85% R.H. a given GMR sensor stack showed no observable corrosion with 96 hours of exposure. (V. V. Doan, C. Chang, C. F. Lam and J. Thompson, “Reliability Characteristics of IrMn Dual Synthetic Spin Valves, IEEE Transactions on Magnetics, Vol. 36, NO. 5, September 2000, pp. 2608-2610). Since corrosive agents are negatively charged, they are repelled by negative voltages. Thus, by holding the GMR sensor at a sufficiently negative voltage, corrosion can be inhibited.

For example, in combination with any of the approaches above, a potential of the sensor may be set at a value below that of a substrate (and/or MR shield and/or writer poles) thereof when a relative humidity in the vicinity of the head or outside a drive housing surrounding the head is above a threshold level. A potential of the sensor may be set at a value of about that of a substrate (and/or MR shield and/or writer poles) thereof when a relative humidity in the vicinity of the head or outside a drive housing surrounding the head is below a second threshold level. The second threshold level may be the same or different than the first threshold level. In addition, the potential of the sensor may be set at a value of about that of a substrate (and/or tape, MR shield and writer poles) thereof when the relative humidity outside a drive housing surrounding the head is below the second threshold level.

Now referring to FIG. 17, a method 1700 for protecting a magnetic head, according to one embodiment, is shown. As an option, the present method 1700 may be implemented in the context of the functionality and architecture of FIG. 14. Of course, the method 1700 may be carried out in any desired environment. It should also be noted that the aforementioned definitions may apply during the present description.

In operation 1702, a relative humidity in a vicinity of a magnetic head may be detected. As previously mentioned, any type of humidity sensor may be used to detect the relative humidity in the vicinity of the head.

In operation 1704, the detected relative humidity may be compared to a threshold level. One or more threshold levels may be used for comparison purposes depending on whether the detected relative humidity is high or low.

In operation 1706, a potential of the sensor may be set at some value relative to that of a substrate thereof (and/or surrounding materials, e.g., tape, MR shield, writer poles, etc.) when the relative humidity in the vicinity of the head based on the comparison.

In yet another embodiment, a potential of the sensor may be set at a value of about that of a substrate (and/or tape, MR shield and writer poles) thereof when the relative humidity in the vicinity of the head is below a threshold level. As mentioned above, this has been found to mitigate shorting.

The potential of the sensor may typically be set, adjusted or maintained irrespective of whether the sensor is in use or not without adversely affecting performance thereof.

In a further approach, during a reading operation, potentials of the sensor and the substrate of the sensor may be set to about a common value irrespective of relative humidity. This reduces the probability of shorting during operation. During an idle period, the potential of the substrate is raised to a level above that of the sensor. This reduces the probability of corrosion. The potential of the sensor during the idle period may be set at either at about a same value as the potential of the sensor during the reading operation, or set higher or lower than the potential of the sensor during the reading operation.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

1. A method for protecting a magnetic head, comprising: reducing a relative humidity in a vicinity of a magnetic head by passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below a threshold level for reducing or eliminating corrosion of the sensor.
 2. The method as recited in claim 1, wherein the elevated bias current is passed through the sensor when the relative humidity in the vicinity of the head is above the threshold level.
 3. The method as recited in claim 2, wherein the elevated bias current is not passed through the sensor when the relative humidity in the vicinity of the head is below the threshold level.
 4. The method as recited in claim 2, further comprising detecting the relative humidity in the vicinity of the head and comparing the detected relative humidity to the threshold level.
 5. The method as recited in claim 1, wherein the elevated bias current is higher than an operating bias current used when the sensor is in use for reading data.
 6. A method for protecting a magnetic head, comprising: during a reading operation, setting potentials of a sensor and a substrate of the sensor to about a common value; and during an idle period, raising the potential of the substrate to a level above that of the sensor.
 7. The method as recited in claim 6, wherein the potential of the sensor during the idle period is set at either at about a same value as the potential of the sensor during the reading operation or lower than the potential of the sensor during the reading operation.
 8. A method for protecting a magnetic head, comprising: detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and if the detected relative humidity is above the threshold level, passing an elevated bias current through a sensor of the head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below the threshold level for reducing or eliminating corrosion of the sensor.
 9. The method as recited in claim 8, wherein the elevated bias current is not passed through the sensor when the relative humidity in the vicinity of the head is below the threshold level.
 10. The method as recited in claim 8, further comprising setting a potential of the sensor at a value below that of a substrate thereof when the relative humidity in the vicinity of the head is above the threshold level.
 11. The method as recited in claim 8, further comprising setting a potential of the sensor at a value below that of a substrate thereof when a relative humidity outside a drive housing surrounding the head is above a second threshold level.
 12. The method as recited in claim 8, further comprising setting a potential of the sensor at a value of about that of a substrate thereof when the relative humidity in a vicinity of the head is below the threshold level.
 13. The method as recited in claim 8, further comprising setting a potential of the sensor at a value of about that of a substrate thereof when a relative humidity outside a drive housing surrounding the head is below a second threshold level.
 14. The method as recited in claim 8, wherein the elevated bias current is higher than an operating bias current used when the sensor is in use for reading data.
 15. A method for protecting a magnetic head, comprising: detecting a relative humidity in a vicinity of a magnetic head; comparing the detected relative humidity to a threshold level; and setting a potential of the sensor at some value relative to the substrate or the surrounding materials based on the comparison.
 16. The method as recited in claim 15, wherein the potential of the sensor is set at a value below that of a substrate thereof when the relative humidity in the vicinity of the head is above the threshold level
 17. The method as recited in claim 15, further comprising reducing the relative humidity in the vicinity of a magnetic head by passing an elevated bias current through a sensor of a magnetic head during at least some time periods when the sensor is not in use for reading data, the elevated bias current being chosen to be sufficient to heat the sensor to a level which will reduce the local relative humidity to below the threshold level for suppressing or eliminating corrosion of the sensor
 18. The method as recited in claim 15, wherein the elevated bias current is passed through the sensor when the relative humidity in the vicinity of the head is above the threshold level.
 19. The method as recited in claim 15, wherein the elevated bias current is not passed through the sensor when the relative humidity in the vicinity of the head is below the threshold level.
 20. The method as recited in claim 15, further comprising setting a potential of the sensor at a value of about that of a substrate thereof when a relative humidity in a vicinity of the head is below the threshold level. 